1. Field of the Invention
The invention relates to silane-modified, water-redispersible polymer powder compositions and the use of these powders in hydraulically setting systems.
2. Description of the Related Art
Polymers based on vinyl esters, vinyl chloride, (meth)acrylate monomers, styrene, butadiene and ethylene are used first and foremost in the form of their aqueous dispersions or water-redispersible polymer powders in a variety of applications, for example as coating compositions or adhesives, for a wide variety of substrates. Dispersion powders are also used as binders in hydraulically setting coatings or in adhesives such as tile adhesives, in TICS mortars (TICS=thermal insulation composite systems), and in plasters and renders or jointing compositions based on cements or gypsum plaster.
It is known from DE 4402408 A1 that water-redispersible dispersion powder compositions can be hydrophobicized by adding water-dispersible organosilicon compounds in the polymerization and subsequently drying the polymer dispersions obtainable in this way by means of spray drying. In DE 4402409 A1, it is proposed that hydrophobicized redispersion powders be obtained by spraying the corresponding polymer dispersion and water-dispersible silicon compounds together. In DE 10040407 A1, polymer dispersions for tile adhesives are modified with silane-containing compounds and with (thio)urea compounds. For this purpose, silane-functionalized and (thio)urea-functionalized monomers are copolymerized or low molecular weight compounds having appropriate functionalities are used. The use of aqueous dispersions of polymers comprising monomer units derived from vinylsilanes for producing adhesive compositions having improved wet adhesion is known from EP 640630 A1. Aqueous polymer dispersions comprising silane-functionalized polymers for use in tile adhesives are also known from DE-A 2148456 and EP 0035332 A2.
In tile production, there is a trend to denser tiles such as fine stoneware tiles or porcelain-like tiles. The water absorption and porosity of these tiles is greatly reduced; in general, their water absorption is less than 0.2% by weight based on the weight of the tile. As a result, the ability of the inorganic binder in the tile adhesive to form a strong bond with the underside of the tile is greatly reduced. The use of a further organic binder, a dispersion powder or a dispersion is necessary in order to improve the adhesion and flexibility of the tile adhesive. To ensure satisfactory adhesive bonding, it is therefore necessary to use ever higher amounts of polymer for stoneware or fine stoneware coverings.